Links

GData - The Objective C Google Data library - XML services. One tiny portion of it is a small, simple wrapper for working with XML on iOS. I use this every day. Includes examples of accesssing each service. For instance: Calendar, Google Docs.

Google Fetcher - wraps NSURLConnection. An easy way to make web requests. I use this every day.

OAuth2 - The Objective C Google OAuth2 library. Manages: UI for asking the user for credentials, securely storing them, and using them to sign HTTP requests. Use this for making requests on Google services where you must be signed in.